Examining the control of differentiation HL-60 cells by phorbol esters helps us to understand both the block to differentiation found in human leukemias and the way in which hormones modulate normal hematopoiesis. We have presented evidence suggesting that specific activation of PK-C isoforms may be necessary to modulate HL-60 differentiation, and that this modulation may involved the differential translocation of specific PK-C isoforms to the nucleus. Once in the nucleus it is possible that PK-C may effect specific transactivating factors to modulate gene transcription and regulate differentiation. We have demonstrated that phorbol ester treatment of HL-60 cells increases the amount of the c-jun RNA which encodes for the transactivator AP-1. Phorbol esters are not physiologic differentiating agents. We have identified a differentiation inducing factor (DIF) which appears to function to differentiate HL-60 cells to macrophages. This 56,000 kDa protein is neither an interferon or interleukin. It will be the goal of this proposal to determine whether activators of HL-60 differentiation stimulate the translocation of specific PK-C isoforms to the nucleus, whether once in the nucleus specific protein phosphorylation occurs, and how differentiation agents effect the activity of specific transactivating proteins. Information gained from the experiments will greatly enhance our knowledge of the mechanisms controlling the differentiation of Hl- 60 cells.